I want to do achive maximum performance and for that i would like to:1)Overclock the CPU. I know it can be done upto 2.7 - 2.8GHz. but don't know how to do it from SLES9.2) Enlarge PCI-Express buffers I need some help on that.

This is out of my area of expertise. I don't use SLES9, but will make a few comments, I hope you don't mind.

Overclocking is a technique for the not-faint-of-heart.

Your system is very nice! Do you really need to overclock it and chance potential stability issues? Overclocking depends on the ability of the system to tolerate this and some experience. Most of the settings that you can use to do this probably are in the bios, where hardware tweaking generally takes place. But, this is so dependent on the ability of the board to be overclocked, the quality of ram in the system and proper cooling, I mean real good cooling in the system. Also, the cpus need to be able to do this and not be locked by the manufacturer, to their actual speed and clock rate.

I'm not aware of any software in Linux to do this. I see that there is monitoring software for this system, but don't see any Linux hardware boosting software.

I would pose this question to the maker of this system/motherboard. Have you asked them?